Is One Subwoofer Really Not Appropriate For 2-Chnl

Consider the trade off; a smallish bookshelf with a set of subs may cost about the same as a larger full range, and the full range, while taking up less room, perhaps, will likely be more coeherent across the entire spectrum.

I tried sub/monitor combos several times over the years and always returned to full range. I found that usually the midrange suffers the most due to the cabinet considerations and size of drivers. However, an exception was the much larger Wharfedale Opus 2-M2 monitor and matching subs. It is a much larger than usual "bookshelf" speaker, which was critical in competing well with its floor standing sibling. You can read it here:


http://dagogo.com/View-Article.asp?bShowUnpublished=&hArticle=759&PageOfArticle=1

As Jim Smith (Get Better Sound) would say, your budget should be spread over two, not one. Having said that, I have two, it is very difficult to set up two, alone one. Expect to work on it for weeks, maybe months. Both should be driven by a single mono signal. A TRA when used properly will be of immense help. The RatShack meter is useless in setting my subs properly.

I too had this question and found the solution with 2 subs. I use Merlin TSM-mme speakers. The sound is amazing, but pipe organ pedal notes and very low bass were just not going to happen.

I purchased one subwoofer and carefully dialed it in. The payoff was better sound, but the system became somewhat directional. The Merlins did not disappear as well before the subwoofer.

I bought a second sub. I placed one sub next to each speaker stand and carefully dialed them in. Now I get the Merlin magic and low bass. My experience is that 2 subs are better than one. Make sure you use the same model subs and they are very high quality.

You only need 1 sub since the very low tones are non-directional, however....the more subs the merrier 2,3,4 to even out the pressure zones in the room. Also, power subs alleviate the current drain on your main amp so the amp can do its very best without strain.

04-18-11: Roscoeiii
Can you point us to a good explanation of how to time align subs and mains?

04-18-11: Stanwal
There is a good set of set up instructions on the Sumiko site.

The Sumiko subwoofer setup instructions can be downloaded here. According to Sumiko...

The optimal position for a REL is in one of the corners behind the main speakers...

No doubt the folks at Sumiko are knowledgeable, but I respectfully disagree with their advice. IMO, placing sub(s) BEHIND the mains may result in good *frequency* response, but it rarely results in good *transient* response.

The reason is because, by placing the sub(s) behind the mains, as Sumiko recommends, the sound from the sub(s) will arrive at the listening position several milliseconds AFTER the sound from the mains. Hence the sub(s) and the mains will not be time aligned.

Some people say that a few milliseconds of time misalignment isn't audible at low frequencies. My experience, and some scientific research, suggest otherwise.

Adjusting the sub's phase will not solve the time misalignment created by placing the sub(s) behind the mains, since the signal that needs to be delayed is NOT the signal for the sub, but rather the signal for the mains. Adjusting sub's phase will do nothing for that.

The time misalignment created by placing the sub(s) behind the mains CAN be solved by digitally delaying the mains. But judging from the systems on A'gon, very few people have that capability. So the most practical way to time align the sub(s) with the mains is...

On the z axis, place the sub(s) roughly coplanar with the mains.

By placing the sub(s) coplanar with the mains, the sound from the sub(s) and the sound from the mains will arrive at the listening position at close to the same time. Hence the sub(s) and the mains will be time aligned, resulting in better transient response. This is audible as better coherence and PRaT.

Keep in mind that subs typically introduce latency into the low-passed signal. Therefore, if you cannot digitally delay the mains, the sub position that results in optimal time alignment will often be slightly IN FRONT of the mains. This is, of course, the *opposite* of what Sumiko recommends.

Another benefit to placing the sub(s) coplanar with the mains is that, in addition to giving better transient response, it will often result in better *frequency* response, for the following reason: Coplanar sub placement minimizes the destructive interference around the crossover frequency. An explanation for why that is so can be read here.

That brings me to Roscoeiii's question about how to time align the sub(s) with the mains. The easiest method is the following…

1. Flip the polarity of either the sub or the mains (but not both).
2. Play a test tone at the crossover frequency.
3. Use an SPL meter to measure the output level.
4. Adjust the sub position (or digital delay, if you have that capability) until you MINIMIZE the SPL at the listening position.
5. When the sub is in place, flip the polarity back so that the sub and the mains are the same polarity.

In steps 1-4, you are essentially maximizing the *destructive* interference between the sub(s) and the mains. In step 5, you are restoring the sub to the correct polarity, which now maximizes the *constructive* interfere between the sub(s) and the mains.

Following this method, the sub(s) should be time aligned with the mains to within about a millisecond or two. You can further improve the time alignment, by adjusting the position of the sub(s) in 1-3 inch increments, searching for the position that results in the best coherence and PRaT. This last step has to be done by ear, so it requires some experience and patience. But it is well worth it, IMO.

You can read more discussion/debate of sub time alignment, transient response, and the limits of human temporal resolution, on another thread.

Hope that helps.

Bryon